Figure 6.

The effect on the addition of glucose (2 μM) and oxygen (10 μM) on N₂ fixation as well as on the nifH gene abundances of the detectable clusters P1, P4 and P7 (both as end point measurements in 24-h incubations, samples from no.3, 95 m) were determined. S.ds. of triplicate measurements are indicated, with the exception of P1 which was below the detection limit in two of three replicate samples. Rates are a minimum value of N₂ fixation due to a probable underestimation by the applied method.